A combustor for a gas turbine may be configured or designed to combust liquid fuels, gaseous fuels or both within a combustion chamber. Pre-filming air-blast liquid fuel injectors for issuing atomized liquid fuel into the combustion chamber of the combustor are well known in the art. In this type of fuel injector, fuel is spread out into a thin continuous sheet and then subjected to a stream of atomizing air.
In one configuration, the atomizing air flows through concentric air swirl passages that generate separate swirling airflows at the nozzle exit. At the same time, liquid fuel flows through a plurality of circumferentially arranged ports and then onto a single or common pre-filming surface where it spreads out into a thin uniform sheet before being discharged from the edge of the pre-filming surface into the cross-flowing air stream. When the fuel is injected into the combustion chamber for combustion, high temperature regions are formed locally in the combustion gas, which increase NOx emissions. The enhanced mixing of the fuel-air combination from the fuel nozzle with the swirling fuel-air mixture in the combustion chamber reduces peak flame temperature within the combustion chamber, thereby reducing NOx emission levels. In addition, water may be injected into the combustion chamber to further reduce cool the flame temperature, thus further reducing NOx emissions levels.
The use of atomizing air to shear the liquid fuel reduces the volume of air that is utilized for other purposes such as cooling the combustor and/or other parts of the gas turbine, thereby affecting the overall efficiency of the gas turbine. In addition, a large volume of water must be supplied at a sufficiently high pressure in order to have sufficient kinetic energy to interacting with the fuel and the atomizing air. This requires high pressure pumps which may also affect the overall efficiency of the gas turbine. Furthermore, use of the atomizing air to atomize the liquid fuel may result in relatively large droplets of fuel that may collect or wet on an inner surface of the combustion liner, thus potentially resulting in spallation and/or degradation of a thermal barrier coating that is typically disposed along the inner surface. Therefore, an improved pre-film liquid fuel cartridge for a combustor of a gas turbine would be useful.